Most known projectile launcher tube systems comprise, as shown in accompanying FIG. 1, a barrel tube 10, a breech or end wall 12 closing the tube 10 at one end, and a pressure source 14 which is generally constituted by a pyrotechnical cartridge.
Before firing, the projectile 20 defines a chamber 16 inside the tube 10, which chamber contains the pyrotechnical cartridge 14.
On firing, explosion of the pyrotechnical cartridge 14 generates driving pressure on the projectile 20 inside said chamber 16. The projectile is set into motion, and the increase in the volume of the chamber 16 causes the gases to expand until the chamber 16 is put into communication with the atmosphere when the projectile 20 leaves the barrel tube 10, as shown diagrammatically in FIG. 2. Over this duration, the integral of pressure multiplied by the sectional area of the barrel tube 10 gives the impulse imparted to the shot.
Such known launch tubes present the drawbacks firstly of generating a large amount of recoil force that is felt by the person firing or by the support of the launch tube, and secondly requires the wall thickness of the tube to be considerable, because of the pressure peak that is generated immediately after the cartridge 14 has exploded. This peak is particularly troublesome for weapons that are fired from the shoulder.
Attempts have already been made to limit the peak recoil force that results from the pressure peak by placing damper means between the launch tube and a reference, e.g. a shoulder piece, or a carriage supporting the launch tube.
Also, in document FR-A-2 713 324, the Applicant has proposed a projectile propulsion assembly of the type comprising a chamber housing a pressure source and communicating with an expansion volume via a passage that is controlled by a servo-control valve enabling the projectile driving pressure to be controlled and preferably adapted to define constant pressure in the expansion chamber.
Document WO-A-91/07636 describes a projectile that includes means for timed ejection of a charge. More precisely, that document describes a launcher comprising a pressure source (not shown) for launching a projectile. The projectile comprises a payload, a first pressure chamber, and a second pressure chamber. A valve feeds the first pressure chamber from the source. The first pressure chamber also communicates with the second pressure chamber via a calibrated orifice. More precisely, the second chamber is defined between a piston that can thrust against the payload and a case defining the first chamber, the piston and the case being interconnected by a shear pin. In addition, according to an essential characteristic of that document, the first chamber is filled with a fibrous material. That projectile operates essentially as follows. During launching, the first chamber is charged at constant pressure via the valve. The pressure in the second chamber rises progressively until the pin shears. The piston then expels the payload with a sudden increase of pressure in the second chamber via the passage thus released by the link between the two pressure chambers.
Document Navy Techn. Disclos. Bull., Vol. III, No. Mar. 3, 1978, Dahlgren Virginia describes a propellant provided on a launch system or on a projectile. That document relates essentially to means for adjusting an area ratio between vents and an orifice leading to the expansion chamber.
Document U.S. Pat. No. 3,628,415 discloses a mortar. It essentially describes means for adjusting the free section of a vent passage. A valve formed by a flap cooperating with the passage serves to evacuate residual moisture from inside the mortar.
Document GB-A-484 346 describes a cartridge containing projectile guide means in the form of a central internal tube. A fraction of the propellant charge is placed inside said tube forming guide means for the projectile and another portion of the propellant charge is disposed outside said guide tube. In this way, in order to guarantee simultaneous initiation of both portions of the propellant charge and also to guarantee equal pressures inside and outside the guide tube, the tube is perforated. Nevertheless, the disposition described in that document does not make it possible in any way to control propulsion pressure, and in particular to maintain it at a value that is at least substantially constant.